[Paper Review] Terahertz brightness at the extreme: demonstration of 5 GV/m, 17 T low frequency {\lambda}3 terahertz bullet

Mostafa Shalaby, C. P. Hauri|arXiv (Cornell University)|Jul 7, 2014

Terahertz technology and applications25 references3 citations

TL;DR

This paper demonstrates a novel terahertz source that achieves extreme brightness by optimizing pump wavefront curvature to produce a diffraction-limited, 3D light bullet confined to a λ³ volume. Using collinearly pumped organic crystals (DSTMS and OH1), the system generates single-cycle terahertz pulses with peak electric fields up to 5 GV/m and 17 T—orders of magnitude higher than previous laser-based sources—enabling new regimes of nonlinear terahertz science.

ABSTRACT

The brightness of a light source defines its applicability to nonlinear phenomena in science. Bright low frequency terahertz (< 5THz) radiation confined to a diffraction-limited spot size is a present hurdle due to the broad bandwidth and long wavelengths associated with single-cycle terahertz pulses as well as due to the lack of terahertz wavefront correctors. Here, using a present-technology system, we employ a new concept of terahertz wavefront manipulation and focusing optimization. We demonstrate a spatio-temporal confinement of terahertz energy at its physical limits to the least possible 3-dimensional light bullet volume of lambda cubic. This leads to a new regime of extremely bright terahertz radiation reaching 40 PW/m2 intensity. The presented work is focused on the sub-5 THz range using small aperture organic crystals DSTMS and OH1. The obtained peak field of up to 5 GV/m and 17 Tesla is order of magnitude higher than any reported single-cycle field oscillation in the entire THz range from a laser-based system and surpassing large scale accelerator systems. The presented results are foreseen to have a great impact on future nonlinear terahertz applications in different science disciplines.

Motivation & Objective

• To overcome the fundamental challenge of low terahertz brightness due to long wavelengths and poor beam quality.
• To demonstrate spatio-temporal confinement of terahertz radiation at the physical limit of λ³ volume.
• To achieve unprecedented field strengths in the sub-5 THz range using compact, laser-based systems.
• To enable new nonlinear terahertz applications by surpassing the field intensity limits of prior laser-driven and accelerator-based sources.

Proposed method

• Employed a 100 Hz Ti:sapphire-based 3-stage optical parametric amplifier (OPA) system with 65±5 fs pulses at 1.35–1.5 µm to pump small organic crystals.
• Used an all-reflective telescope to control the pump beam's wavefront curvature at the nonlinear crystal, minimizing wavefront aberrations.
• Selected highly efficient organic crystals (DSTMS and OH1) with high nonlinearity (214–240 pm/V) and high damage thresholds (~20 mJ/cm²).
• Applied off-axis mirrors for THz beam expansion and focusing, achieving near-diffraction-limited beam quality.
• Used microbolometer imaging and calibrated intensity measurements to determine spot size and peak field from pulse energy and duration.
• Employed both electro-optic sampling (EOS) and ABCD detection to validate temporal and spectral characteristics of the generated pulses.

Experimental results

Research questions

• RQ1 Can terahertz wavefront aberrations be corrected sufficiently in a laser-based system to achieve diffraction-limited focusing?
• RQ2 What is the maximum achievable electric field strength in a single-cycle terahertz pulse using current compact laser technology?
• RQ3 To what extent can terahertz brightness be enhanced by optimizing pump beam wavefront curvature in organic nonlinear crystals?
• RQ4 How does spatio-temporal confinement to a λ³ volume affect the temporal and spectral profile of terahertz pulses?
• RQ5 Can field strengths exceeding 5 GV/m be achieved in the sub-5 THz range with a table-top laser system?

Key findings

• The system achieved a peak electric field of 5 GV/m and 17 T in the sub-5 THz range, representing an order-of-magnitude increase over previous laser-based sources.
• The terahertz radiation was confined to a 3D volume of approximately λ³, achieving extreme brightness with an intensity of up to 40 PW/m².
• The wavefront control via pump beam curvature optimization led to a nearly perfect THz wavefront, enabling diffraction-limited focusing.
• The measured THz pulses exhibited significant spectral modulation due to phonon resonances in DSTMS (1.024 THz) and OH1 (1.45, 2.85, and ~4.9 THz), which shaped the spectral envelope.
• The use of collinear pumping in organic crystals preserved beam symmetry and quality, enabling superior focusing compared to non-collinear schemes.
• The results surpass both conventional laser-driven sources and large-scale accelerator systems in peak field strength for single-cycle pulses.